Search results for "NOISE"
showing 10 items of 1375 documents
The role of noise on the steady state distributions of phytoplankton populations
2016
The spatio-temporal behaviour of total chlorophyll concentration is investigated in the middle of the Tyrrhenian Sea by using a stochastic approach. The study is based on a reaction-diffusion-taxis model, which is used to analyse the dynamics of five phytoplankton groups, responsible for about 80% of the total chlorophyll a inside the euphotic zone of the water column. The analysis is performed by considering: (i) the intraspecific competition of the phytoplanktonic groups for limiting factors, i.e. light intensity and nutrient concentration, (ii) the seasonal changes of environmental variables, and (iii) the random fluctuations of the components of the velocity field and temperature. Speci…
The irreducible uncertainty of the demography–environment interaction in ecology
2002
The interpretation of ecological data has been greatly improved by bridging the gap between ecological and statistical models. The major challenge is to separate competing hypotheses concerning demography, or other ecological relationships, and environmental variability (noise). In this paper we demonstrate that this may be an arduous, if not impossible, task. It is the lack of adequate ecological theory, rather than statistical sophistication, which leads to this problem. A reconstruction of underlying ecological processes can only be done if we are certain of either the demographic or the noise model, which is something that can only be achieved by an improved theory of stochastic ecologi…
The effect of low frequency noise on the behaviour of juvenile Sparus aurata.
2020
[EN] Anthropogenic activities are causing increased noise levels in the marine environment. To date, few studies have been undertaken to investigate the effects of different noise frequencies on the behaviour of juvenile fish. In this study, the behavioural changes of juvenile gilthead seabream (Sparus aurata) are evaluated when exposed to white noise filtered in third-octave bands centred at 63, 125, 500, and 1000 Hz (sound pressure level, 140-150 dB re 1 mu& x3a1;a) for 7 h. The group dispersion, motility, and swimming height of the fish were analysed before and during the acoustic emission. Dispersion of the fish was found to reduce immediately upon application of low frequency sound (63…
Context-dependent coloration of prey and predator decision making in contrasting light environments
2022
A big question in behavioral ecology is what drives diversity of color signals. One possible explanation is that environmental conditions, such as light environment, may alter visual signaling of prey, which could affect predator decision-making. Here, we tested the context-dependent predator selection on prey coloration. In the first experiment, we tested detectability of artificial visual stimuli to blue tits (Cyanistes caeruleus) by manipulating stimulus luminance and chromatic context of the background. We expected the presence of the chromatic context to facilitate faster target detection. As expected, blue tits found targets on chromatic yellow background faster than on achromatic gre…
Non-linear biological responses to disturbance: consequences on population dynamics
2003
Abstract We assessed how non-linear biological responses to environmental noise, or “noise filtering”, impact the spectra of density-dependent population dynamics, and the correlation between noise and population dynamics. The noise was assumed to affect population growth rate in a discrete-time population model by Hassell [J. Anim. Ecol. 44 (1975) 283–295] where the population growth rate was linked to the environment with an optimum type filter. When compared to unfiltered noise, the filtered noise can distort the stationary distribution of population values. The optimum type filter can make cyclic population dynamics more regular and low population values can become more frequent or rare…
Is the impact of environmental noise visible in the dynamics of age-structured populations?
2001
Climate change has ignited lively research into its impact on various population–level processes. The research agenda in ecology says that some of the fluctuations in population size are accountable for by the external noise (e.g. weather) modulating the dynamics of populations. We obeyed the agenda by assuming population growth after a resource–limited Leslie matrix model in an age–structured population. The renewal process was disturbed by superimposing noise on the development of numbers in one or several age groups. We constructed models for iteroparous and semelparous breeders so that, for both categories, the population growth rate was matching. We analysed how the modulated populatio…
Whistling is metabolically cheap for communicating bottlenose dolphins (Tursiops truncatus)
2020
Toothed whales depend on sound for communication and foraging, making them potentially vulnerable to acoustic masking from increasing anthropogenic noise. Masking effects may be ameliorated by higher amplitudes or rates of calling, but such acoustic compensation mechanisms may incur energetic costs if sound production is expensive. The costs of whistling in bottlenose dolphins (Tursiops truncatus) have been reported to be much higher (20-50% of resting metabolic rate, RMR) than theoretical predictions (0.5-1% of RMR). Here we address this dichotomy by measuring the change in the resting O2 consumption rate (V̇O2), a proxy for RMR, in three post-absorptive bottlenose dolphins during whistlin…
5G IoT system for real-time psycho-acoustic soundscape monitoring in smart cities
2020
In Next-Generation Technologies, the monitoring of environmental noise nuisance in the Smart City should be as efficient as possible. 5G IoT systems offer a great opportunity to offload the node calculation, as they provide a number of new concepts for dynamic computing that previous technologies did not offer. In this case, a complete 5G IoT system for psycho-acoustic monitoring has been implemented using different options to offload the calculation of the parameters to different parts of the system. This offloading has been implemented by directly computing the metrics in the node (as a Raspberry Pi), and in a ESP32 device (FiPy) and by sampling the audio and sending it to the EDGE in the…
Phase-noise Impact on the Performance of mmWave-radars
2019
The impact of phase noise in Frequency Modulated Continuous Wave (FMCW) millimeter-wave (mmWave) radars is investigated in this paper. A FMCW signal is transmitted from the radar, reflected off a moving object and processed at a receiver in the radar. The impact of random phase noise/jitter on the performance parameters of estimated distance, speed and angle of arrival of an object is studied. Our studies show that there exists a threshold at about fifteen percent of the period of the carrier frequency, over which errors substantially manifest in the estimations. Distance estimation is less affected than speed and angle, which rely directly on the phase information for the estimations. Angl…
Adaptive-gain extended Kalman filter: Extension to the continuous-discrete case
2009
In the present article we propose a nonlinear observer that merges the behaviors 1) of an extended Kalman filter, mainly designed to smooth off noise , and 2) of high-gain observers devoted to handle large perturbations in the state estimation. We specifically aim at continuous-discrete systems. The strategy consists in letting the high-gain self adapt according to the innovation. We define innovation computed over a time window and justify its usage via an important lemma. We prove the general convergence of the resulting observer.